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Gollnick, Nicole Severine (2008): Survival of different Mycobacterium avium subsp. paratuberculosis strains in bovine monocyte-derived macrophages. Dissertation, LMU München: Faculty of Veterinary Medicine
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Abstract

In this study the ability of different Mycobacterium avium subsp. paratuberculosis (M. paratuberculosis) strains to survive in bovine monocyte-derived macrophages (MDMs) was investigated. The following hypotheses were tested: 1) Infection status of a cow does not affect the ability of its macrophages to kill M. paratuberculosis 2) Killing capacity of bovine macrophages is not dependent on the M. paratuberculosis strain MDMs for conducted experiments were obtained from Johne’s disease-positive (n = 3) and age and stage of lactation matched Johne’s disease-negative (n = 3) multiparious cows. Animals were kept on the same dairy operation, thus non-infected cows had been exposed to M. paratuberculosis strains present on the farm premises. Peripheral blood mononuclear cells (PBMC) were isolated from whole blood by density gradient centrifugation. After a five-day differentiation period in cell culture using Teflon jars MDMs were obtained and subsequently challenged in vitro with four M. paratuberculosis strains of different host specificity (bovine, ovine). MDMs were harvested at 2 hours, 2 days, 4 days and 7 days following infection. For each time point ingestion and intracellular survival of M. paratuberculosis strains were determined by fluorescence microscopy. There was no effect of the origin of MDMs (Johne’s disease-positive or control animals) on phagocytosis, survival of bacteria, or macrophage survival. In contrast, important strain differences were observed. These findings suggest that some M. paratuberculosis strains interfere more successfully than others with the ability of macrophages to kill intracellular pathogens which may make it important to include strain typing when designing control programs.